eloso

You don't want to do that there not going to do what you think. One will try to put out more the it should and basically cutoff the second one. See there not going to supply the same voltage.

I would do this use a PNP to get you more current

Here's a circuit that I use for more regulated power... the small resistor values cause the 78XX part to provide current limit (around 10 amps with these values) and since the regulator and pass transistor are on the same heatsink, the thermal protection of the 78XX is also provided.

Note the way the output is connected... this provides remote current sensing which compensates for drop along long wires if they are used.

Only disadvantage to this circuit is that a minimum load of a few milliamps is required because of the design of the 78XX regulator. If you use an LM-317 instead, then this is not a problem.

(edit to add): If you use a 79XX regulator and an NPN 2N3055 and reverse the plus and minus terminals, you get the same circuit.

http://www.wikihow.com/Convert-a-Computer-ATX-Power-Supply-to-a-Lab-Power-SupplyAs much problems your having find you a old PSU from a computer kind with a switch to turn on and use thatmost have up to 30 amp output on 5 volt and about half of that on the 12 volt.

eloso

You don't want to do that there not going to do what you think. One will try to put out more the it should and basically cutoff the second one. See there not going to supply the same voltage.

I would do this use a PNP to get you more current

Here's a circuit that I use for more regulated power... the small resistor values cause the 78XX part to provide current limit (around 10 amps with these values) and since the regulator and pass transistor are on the same heatsink, the thermal protection of the 78XX is also provided.

Note the way the output is connected... this provides remote current sensing which compensates for drop along long wires if they are used.

Only disadvantage to this circuit is that a minimum load of a few milliamps is required because of the design of the 78XX regulator. If you use an LM-317 instead, then this is not a problem.

(edit to add): If you use a 79XX regulator and an NPN 2N3055 and reverse the plus and minus terminals, you get the same circuit.

You can buffer that pnp with a power npn / n-ch mosfet so you can use a smaller pnp device instead.

No it doesn't. It's chosen so that when the load is around 10 amps, the load that the 78xx sees is 1 amp. The idea is to carry over the current limit and thermal protection built into the 78xx without needing extra components.

I've been using this circuit for literally decades... believe me, it works.

so the regulator can be very hot at 700mA? i almost got skin burned when i touched it. Im using tip42c pnp.

Note that my drawing shows both the regulator and pass transistor on the same heatsink. The idea is for both devices to share the same temperature... that way if the pass transistor gets too hot, it heats the 78xx regulator and trips the thermal protection. The circuit is designed to pass along the current limiting and thermal protection of the 78xx regulator to the pass transistor.